Usually, touch screen panels are input devices which are respectively attached onto display devices such as LCDs (Liquid Crystal Displays), PDPs (Plasma Display Panels), OLED (Organic Light Emitting Diode) displays, and AMOLED (Active Matrix Organic Light Emitting Diode) displays, to thus generate an input signal corresponding to a position where an object such as a finger or a touch pen is touched on the touch screen panel. The touch screen panels are widely used in various fields of mobile devices such as small-sized portable mobile phones, industrial terminal devices, and DIDs (Digital information Devices).
Various types of conventional touch screen panels are disclosed, but resistive type touch screen panels having simple manufacturing processes and inexpensive manufacturing costs have been used most widely. The resistive type touch screen panels, however, have a low transmittance and undergo a pressure to be applied, respectively, to thereby cause an inconvenient use. The resistive type touch screen panels also have difficulties in recognizing multiple touches and gestures, and cause detection errors.
In contrast, capacitive touch screen panels may have a high transmittance, recognize soft touches, and recognize multiple touches and gestures satisfactorily, to thus widen a market share gradually.
FIG. 1 shows an example of the structure of a conventional capacitive touch screen panel. Referring to FIG. 1, in the conventional capacitive touch screen panel, transparent conductive films are respectively formed on the top and bottom surfaces of a transparent substrate 2 made of plastic or glass. Metal electrodes 4 for applying a voltage are formed at each of four corners of the transparent substrate 2. The transparent conductive film is formed of transparent metal such as ITO (Indium Tin Oxide) or ATO (Antimony Tin Oxide). The metal electrodes 4 respectively formed at the four corners of the transparent conductive film are formed by printing low resistivity conductive metal such as silver (Ag). A resistor network is formed around the metal electrodes 4. The resistor network is formed in a linearization pattern in order to transmit a control signal equally on the entire surface of the transparent conductive film. A protective film is coated on top of the transparent conductive film including the metal electrodes 4.
In the case of the capacitive touch screen panel, when a high-frequency alternating-current (AC) voltage is applied to the metal electrodes 4, the high-frequency alternating-current (AC) voltage is spread to the whole surface of the transparent substrate 2. Here, if a finger 8 or a conductive touch input unit lightly touches the top surface of the transparent conductive film on the transparent substrate 2, a certain amount of electric current is absorbed into the human body and a change in the electric current is detected by a built-in electric current sensor of a controller 6, to thus calculate the amount of electric current at the four metal electrode 4, respectively, and to thereby recognize a touch point.
However, the capacitive touch screen panel shown in FIG. 1 detects the amount of micro-current, and requires an expensive detecting device, to thus raise the price of the capacitive touch screen panel, and make it difficult to recognize multiple touches.
In recent years, in order to overcome such problems, the capacitive touch screen panel shown in FIG. 2 has been chiefly used. The touch screen panel of FIG. 2 includes a transverse linear touch pad 5a, a longitudinal linear touch pad 5b, and a touch drive IC (Integrated Circuit) 7 for analyzing a touch signal. The touch screen panel detects a magnitude of a capacitance that is formed between the linear touch pad 5 and the finger 8. Here, the touch screen panel scans the transverse linear touch pad 5a and the longitudinal linear touch pad 5b to thus detect a touch signal and to thereby recognize a plurality of touch points.
However, when the touch screen panel is mounted on a display device such as a liquid crystal display (LCD) and is used, it may be difficult to detect a signal due to noise. For example, the liquid crystal display (LCD) uses a common electrode and an alternating-current (AC) common voltage (Vcom) is applied the common electrode in some cases. The common voltage Vcom of the common electrode acts as noise when detecting touch points.
FIG. 3 shows an example in which a conventional capacitive touch screen panel is installed on a liquid crystal display (LCD). A display device 200 such as the liquid crystal display (LCD) has a structure that liquid crystal is sealed and filled between a lower-side thin film transistor (TFT) substrate 205 and an upper-side color filter 215 to thereby form a liquid crystal layer 210. To seal the liquid crystal, the TFT substrate 205 and the color filter 215 are joined by sealants 230 at their outer portions. Although they are not shown, polarizing plates are attached on the top and bottom of the LCD panel, and besides back light units (BLUs) are provided.
As shown, a touch screen panel is provided on top of the display device 200. The touch screen panel has a structure that the linear touch pad 5 is put on the upper surface of the substrate 1. A protection panel 3 for protecting the linear touch pad 5 is attached on top of the substrate 1. The touch screen panel is bonded to the edge portion of the display device 200 through the medium of an adhesive member 9 such as a double adhesive tape (DAT), and an air gap 9a is formed between the display device 200 and the touch screen panel.
In this configuration, if a touch occurs as shown in FIG. 3, a capacitance Ct is formed between the finger 8 and the linear touch pad 5. Meanwhile, as shown, a capacitance Cvcom is formed between the linear touch pad 5 and a common electrode 220 formed on the lower surface of the color filter 215 of the display device 200, and an unknown parasitic capacitance Cp due to capacitive couplings between patterns or manufacturing process factors also functions at the linear touch pad 5. Thus, the same circuit as an equivalent circuit of FIG. 4 is configured.
Here, the conventional touch screen panel recognizes a touch by detecting an amount of change in the capacitance Ct, where the components such as the capacitances Cvcom and Cp act as noise at the time of detecting the capacitance Ct. For example, small- and medium-sized LCDs for mobile devices employ a line inversion method in which the common voltage Vcom of the common electrode 220 alternates by one or a plurality of gate lines as shown in FIG. 5, in order to reduce current consumption, and thus the alternating electric field acts as considerable noise at the time of detection of touches.
Typically, in order to remove the noise, the air gap 9a is placed between the touch screen panel and the display device 200 as shown in FIG. 3. In addition, although it is not shown, an ITO layer is coated on the lower surface of the substrate 1 of the touch screen panel, to thereby form a shield layer. In addition, the shield layer is grounded with the ground signal.
However, in the case of the conventional art, products become thick and the quality of the products deteriorates due to the air gap 9a. In addition, the conventional art requires a separate shield layer and a manufacturing process of configuring the shield layer, thereby causing a rise of a manufacturing cost. In particular, in the case of forming a built-in touch screen panel in a liquid crystal display (LCD), it is very difficult to form the air gap 9a or the shield layer, and thus it is also very difficult to form the built-in touch screen panel in a display device such as the liquid crystal display (LCD).